1) Field of the Invention
This invention relates generally to fabrication of semiconductor devices and more particularly to patterning semiconductor devices with resolution down to 0.12 .mu.m on a silicon substrate using oxynitride film.
2) Description of the Prior Art
The semiconductor industry's continuing drive toward semiconductor devices with ever decreasing geometries coupled with the reflective property of monocrystalline silicon and polycrystalline silicon (polysilicon, poly) have led to increasing photolithographic patterning problems. Unwanted reflections from the underlying nonocrystalline silicon or polycrystalline silicon during the photolithographic patterning process cause the resulting photoresist patterns to be distorted. Diffraction of the light waves used to expose the photoresist during patterning also causes distortion of the resulting patterns.
Organic and inorganic bottom anti-reflective coatings have been attempted on both monocrystalline silicon and polycrystalline silicon to absorb reflected energy and prevent pattern distortion. However, different film thicknesses due to surface topography after coating will cause etching issues, photoresist loss and poor after etch inspection (AEI) dimensions.
Phase-shifting masks have been used to compensate for diffraction and enhance the resolution of photolithographic patterns. A phase shift layer is used to cover one of a pair of adjacent apertures of the pattern mask during exposure. The phase shifting layer reverses the sign of the electric field of its aperture. The distortions of the electric field from adjacent appertures caused by diffraction cancel because they have opposite signs. The phase change is a function of wavelength and thickness of the transparent phase shifting layer. However, phase shifting masks do not prevent distortion from reflections.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering the following patents.
U.S. Pat. No. 5,600,165 (Tsukamoto et al.) shows a SiON layer as a bottom ARC over several different structures, including polysilicon, oxide, and silicides.
U.S. Pat. No. 5,639,687 (Roman et al.) shows a Si-rich SiON ARC layer in which thickness (t) is determined as a function of wavelength (.lambda.) and refractive index (n) using the formula t=.lambda./4n.
U.S. Pat. No. 5,252,515 (Tsai et al.) teaches a process for forming SiON ARC layer with refractive index (n) of between 1.5 and 2.1 by controlling the silane flow rate.
U.S. Pat. No. 4,717,631 (Kaganowicz et al.) shows a SiON passivation layer having a refractive index (n) of between 1.55 and 1.75 at a wavelength (.lambda.) of 632.8 nm.